Bagchi Suvendra N, Bitz Tatjana, Pistorius Elfriede K, Michel Klaus-Peter
BioVIII: Lehrstuhl für Molekulare Zellphysiologie, Fakultät für Biologie, Universität Bielefeld, Universitätsstr. 25, Bielefeld, 33615, Germany.
Photosynth Res. 2007 Apr;92(1):87-101. doi: 10.1007/s11120-007-9176-y. Epub 2007 Jun 7.
Following a N-methyl-N'-nitro-N-nitrosoguanidine-based mutagenesis of Synechococcus elongatus PCC 7942 wild type, we were able to select several mutants with an enhanced tolerance toward the herbicide bentazone (3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one 2,2-dioxide). Mutant Mu1 has in part been previously characterized. In the present paper we report on another mutant, called Mu2, which also has a higher tolerance toward bentazone. Since Mu2 showed a better growth than WT when cultivated with elevated NaCl concentrations in the growth medium and since S. elongatus WT has previously been classified to be low salt tolerant, we were especially interested in the identification of the modifications conferring this higher salt tolerance to mutant Mu2. Immunoblot analyses provided evidence that Mu2 had a constitutively higher expression of PsbO and of IsiA. In addition, in Mu2 a significantly higher concentration of IdiA was detected under salt stress as compared to WT. These three proteins most likely contribute to a better protection and/or stabilization of photosystem II. Moreover, Mu2 had a higher amount of the photosystem I reaction center proteins PsaAB under salt stress than WT. In addition, the amount of the ferredoxin:NADP+ oxidoreductase and also of the ATP synthase was constitutively higher in Mu2 than in WT. In contrast to WT the latter two proteins did not decrease under salt stress in Mu2. Therefore, it can be assumed that Mu2 could maintain a high cyclic electron transport activity around photosystem I under salt stress. It can be assumed that the combination of these modifications of the electron transport chain cause a better protection of photosystem II against oxidative damage and cause an increase of cyclic electron transport activity around photosystem I with ATP synthesis. Thus, the overall cellular energization in Mu2 relative to WT is improved. Together with putative other not yet identified modifications this seems to enable Mu2 to energize its cytoplasmic membrane-localized ion pumps more effectively than WT and, as a consequence, to keep the intracellular NaCl concentration low.
在用基于N-甲基-N'-硝基-N-亚硝基胍对聚球藻PCC 7942野生型进行诱变后，我们能够筛选出几个对除草剂苯达松（3-异丙基-1H-2,1,3-苯并噻二嗪-4(3H)-酮2,2-二氧化物）耐受性增强的突变体。突变体Mu1部分特性先前已有报道。在本文中，我们报道了另一个名为Mu2的突变体，它对苯达松也具有更高的耐受性。由于在生长培养基中添加较高浓度NaCl培养时，Mu2比野生型生长得更好，且聚球藻野生型先前被归类为耐盐性低，因此我们特别关注确定赋予突变体Mu2更高耐盐性的修饰。免疫印迹分析表明，Mu2中PsbO和IsiA的表达持续较高。此外，与野生型相比，在盐胁迫下Mu2中IdiA的浓度显著更高。这三种蛋白质很可能有助于更好地保护和/或稳定光系统II。此外，在盐胁迫下，Mu2中光系统I反应中心蛋白PsaAB的含量比野生型更高。此外，Mu2中铁氧还蛋白：NADP +氧化还原酶以及ATP合酶的含量持续高于野生型。与野生型不同，后两种蛋白质在Mu2中盐胁迫下没有减少。因此，可以推测Mu2在盐胁迫下能够维持围绕光系统I的高循环电子传递活性。可以推测，电子传递链的这些修饰组合可更好地保护光系统II免受氧化损伤，并导致围绕光系统I的循环电子传递活性增加以及ATP合成增加。因此，相对于野生型，Mu2中的整体细胞能量供应得到改善。与推测的其他尚未确定的修饰一起，这似乎使Mu2能够比野生型更有效地为其细胞质膜定位的离子泵提供能量，从而使细胞内NaCl浓度保持较低。
